This invention relates to apparatus for conveying panels; more in particular the apparatus according to the invention is a conveyor belt destined to convey in a longitudinal transfer direction electric circuit panels and comprises two endless conveyor belt members revolving spaced from, and in parallel with each other, which endless members can consist of belts, ropes, chains or the like; a charging station, a discharging station, and a random number of working stations therebetween, through which the panels are to be transferred by the conveyor belt; and panel-engaging devices associated with the endless conveyor belt members and spaced from each other in sequence at determined intervals which engaging means are adapted for gripping successively rims of the panels, on opposite sides thereof, at the charging station, and thus holding the gripped panels while transferring them past the working stations to the discharging station and releasing the panels again in the latter station.
The conveyance of panels having sensitive surfaces always presents a problem. This is particularly true in the case of freshly coated circuit panels which are to be transferred from a coating station to a drying station. The panels are first provided with conductive paths, whereupon a coat of protective varnish is applied to one panel surface. The varnish layer is then dried, exposed to light and the lighted areas are developed, whereby the conductive path is exposed at certain points which can then be electrically contacted.
In order to coat the panel, it must be cleaned, preheated and a layer of the protective varnish applied to one side thereof; the varnish solvent is then evaporated (e.g. by passing an air stream past the coated surface) and finally the coated panel is transferred to an oven for drying. The same procedure of pre-heating, coating, evaporation of solvent by ventilating air, and drying is then repeated to a varnish coating on the opposite surface of the panel. The panel is then again exposed with its other surface, developed and finally dried in the oven.
The automatic transfer of the circuit panels on the conveyor apparatus is problematic particularly when the second surface of the panel is to be coated, and most particularly during the heating phase. Heating does, of course, greatly soften the varnish and renders it particularly sensitive to touch, e.g. by mechanical parts of the apparatus. Conventional conveying apparatus such as conveyor belts supporting the panels would injure the varnish layer to an inadmissible degree, leading to deformation of the supported areas and to contamination with dirt, dust, grease and the like.
For this reason, a known conveying apparatus comprises two conveyor belts revolving in parallel in such position that their cross sections form together a V pointing downwardly, so that the panels being transferred only contact the upper marginal zones of the V. However, particularly these panels tend to bend and thus come to rest on broader zones of the two conveyor belts, thereby damaging the varnish layer on the underside of the panel and rendering it unfit for its protective purpose.
Therefore, conveyor apparatus were developed which comprise gripping means mounted on the conveyor chains and adapted for clamping-in the panel margins. These gripping means comprise a relatively complicated automatic clamping mechanism. Particularly, when panels of varying width are to be transferred, the relative position of the chains bearing the gripping means must be re-adjusted each time a panel of different width, transverse to the direction of transfer, is to be taken up by the conveyor, thus interrupting each time the work process.
Further problems are caused by panels having a certain twist, i.e. where the panel surface does not extend in a straight horizontal plane. These panels must be turned by a specially provided guiding system so that they can be inserted in the gripping means of which those positioned on opposite belt members face each other, and those adjacent each other on one and the same belt member are also located, in a common straight flat plane. Moreover, a safe grip of these known gripping means is not guaranteed in the manner independently of the weight and thickness of the panels. In this connection, it must be taken into account that the thickness of the panels and their flexibility will continuously vary as the temperature of the panel changes.
Finally, it should be mentioned that gripping means of known construction tend to become clogged by softened varnish and to bind after several runs of panels therethrough.